This application claims the priority benefit of Japanese application serial no. 2001-285122 filed on Sep. 19, 2001.
1. Field of the Invention
This invention relates generally to a fixing device and an image forming device, which can be used in a facsimile device, a printer, a copier, or a multi-function machine with the above functions.
2. Description of Related Art
FIG. 3, is a side view showing an internal structure of a facsimile apparatus comprising a conventional fixing device and a conventional image forming device. The facsimile apparatus comprises a facsimile main body 1, a process cartridge 2, a photo-sensing unit 3 having the process cartridge, an optical writing device 4, a paper-feeding cassette 5 for storing the recording paper, a paper-feeding roller 6 for feeding the recording paper from the paper-feeding cassette 5, a transcribing roller 7, a fixing device 8 consisting of a fixing roller 9 and a pressure roller 10, which is used for fixing the toner image onto the recording paper, an ejecting roller 11, a sealed sensor 12, and a document stage 13 disposed above the facsimile main body 1. The process cartridge 2 comprises various processing devices for performing the image formation by an electronic photographic process, and is detachable from the facsimile main body 1. The optical writing device 4 makes the photo-sensing unit 3 to scan by using a laser beam that is modulated based on the image data. The transcribing roller 7 is in contact with the photo-sensing unit 3 for transcribing the toner image formed on the photo-sensing unit 3 onto the recording paper.
The document placed on the document stage 13 is passed through the surface of the sealed sensor 12 by a transport system, and then ejected out into an external document stage. As the document passes through the surface of the sealed sensor 12, the image on the document is optically read by the sealed sensor 12. The image data, which is read by the sealed sensor 12 or input from an external source, is transmitted to the optical writing device 4. Based on the image data, the optical writing device 4 emits a modulated laser beam to the surface of the uniformly charged photo-sensing unit 3, so that an electrostatic latent image is formed on the surface of the photo-sensing unit 3. Then, the toner is made to adhere to the electrostatic latent image to form a toner image, and the toner image is transcribed onto the recording paper by the transcribing roller 7. As the recording paper passes through a nip portion between the fixing roller 9 and the pressure roller, by pressing and heating from the fixing device 8, the toner image is fixed onto the recording paper. Next, the recording paper is ejected out into an external document plate by the paper-ejecting roller 9.
Conventionally, an infrared heater or a halogen heater is used as the fixing heater in the fixing device. A structure constituting a fuser roller and a pressure roller pair is most commonly used in the conventional art. Typically, a conventional pressure roller is constructed by forming a silicon rubber layer on a core bar and then forming a mold-releasing layer (such as a tube made of fluorine resin) on the silicon rubber layer, so that the thermal capacity of the pressing roller can be increased. At the beginning of a heating process, the pressure roller does not get warmed-up easily, which causes incomplete fixing problems.
Instead of the pressure roller, a nip portion is formed by pressing a sheet-shaped pressure unit to be in contact with the fixing roller. For example, a fixing device for fixing an un-fixed image onto the recording paper by making the recording paper to pass through the nip portion is well studied and researched. Therefore, the sheet can be easily warmed up, and the heating efficiency can be higher compared to the device using a pressure roller.
A sheet shaped pressure unit is also used for applying pressure onto the recording paper. But the sheet-shaped pressure unit is not elastic, therefore causes a loading weight on the recording paper as the recording paper passes through the fixing device. It is preferred that the sheet-shaped pressure unit has a thermal resistance and a surface having less friction. On the other hand, in fixing device, in order to stabilize and effectively transport the recording paper, the surface of the fixing device, which a friction force is created thereon, can provide a transporting force. But, as the surface of the fixing roller becomes rougher, the toner is easily adhered on the surface of the fixing roller.
Accordingly, it is an object of the present invention is to provide a fixing device and an image forming device, which eliminate or substantially reduce the foregoing problems described above. Specially, this invention provides a fixing device with a capability of reducing the toner""s adhesion onto the fixing roller and also capable of improving the transportation of the recording paper.
In order to achieve the above object and other objects of the present invention, a fixing device is provided. The fixing device comprises a fixing unit, heated by a heating source; and a sheet-shaped pressure unit, having elastic characteristics and in contact under a pressure with the fixing unit. In operation, as a recording paper with a toner image transcribed thereon passes through a nip portion between the sheet-shaped pressure unit and the fixing unit, due to pressing and heating effects, the toner image is fixed onto the recording paper. In addition, a surface layer is formed on a surface of the fixing unit, wherein the surface layer comprises a material capable of increasing a friction coefficient. Further, the surface layer has a water contact angle as a wettability, which is greater than or equal to 90xc2x0, therefore the wettability of the surface layer is small. Because the surface friction coefficient of the fuser roller is increased, therefore when the recording paper with a transcribed toner image passes between the fixing unit and the sheet-shaped pressure unit, a transporting force can be effectively created at a front end of the recording paper. Thus, the recording paper can pass firmly. Furthermore, because the water contact angle is above 90xc2x0, the toner adhesion onto the fixing roller surface can be effectively reduced.
Additionally, according to one aspect of the present invention, the surface layer is formed by PTFE having a glass fiber, a graphite, or a bronze, filled therein. By using this structure, the surface friction coefficient of the fixing roller can be increased.
The invention further provides an image forming device, which comprises the above fixing device. By using this structure, the transporting property of the recording paper can be improved.